There are somewhere between
250 million and 300 million people
wearing them. Most people wear
contact lenses quite comfortably.

But a very small 0.0001 per cent,
which is still a number of people,
run into problems.

One problem we are particularly
interested in is that some people
get feelings of discomfort, as
though they have another condition
called dry eyes.

How do you know if contact lenses
affect the eyes?

We feel that tears can shed light
on this. Across the surface of your
cornea is a layer of fluid that contains
different types of proteins,
and which is only 15 microns thick.

When you look at my eyes or anyone’s
eyes, you are looking right
through the tears. In a way, it is not
even the cornea that influences the
light, it is the tear layer. So having a
proper tear layer on top of the
cornea ends up focusing light very
accurately onto your retina.

Some of the problems that you
can imagine happening with the
tear layer can then happen with
the cornea.

We have done studies looking at
contact lenses and know oxygen
passes pretty well through most
contact lenses nowadays. But do
the cells of your eye feel anything?
And the fact is, they do, they really
seem to.

How do you study tears?

We start with two methods of collection.
One is the standard clinical
procedure called the Type-1
Schirmer’s test using a standardised
strip of filter paper. You hook it
over the eyelid and you close your
eyes and the tears get absorbed
onto the piece of filter paper.

The other way we do it is by using
a small micro-capillary tube. We collect
anywhere from one to five micro-
litres of tears through this
method. But for people with dry
eyes, this is really too much, so we
use the filter paper because it is easier
for them.

We then dilute the tears a bit and
remove any debris or dead cells in
the tears. The proteins in the sample
are then identified using machines
from Sciex – a life science
and analytical technologies firm –
which are hooked up to different
protein databases.

How do contact lenses affect the
tear layer?

Contact lenses change the constituents
in the tear layer. In a
normal eye, there are different
constituents coming from different
sources.

In people who wear contact
lenses, we find there is a bit more of
an inflammatory nature to the molecules
floating around in the tears.

So (this causes) a little bit of irritation irritation.
This occurs after wearing the
lenses for only about three hours. It
varies from person to person but
the best way to avoid all this is to
use daily disposable lenses.

What causes the irritation?

We can tell that the cells in the
cornea showed signs that they were
not getting as much oxygen as they
were getting before. It is not a
change that makes them die, but
changes their physiology. What’s
the long-term outcome of that? We
don’t really know. But we know
cells will adapt to conditions. Probably
what’s happening is the cells are
getting used to the conditions in
your eye. They don’t die but they
change how they function a little
bit to adapt to the new conditions.

Can this change eventually cause
damage?

In most people, no, but in a few
people it might. It might temporarily
change the thickness of the cornea;
the cornea might absorb a bit more
water but, after a while, it will pump
that out. In most people, the cells
adapt, and they do fine. Once in a
while, there might be somebody
whose cells don’t adapt as well. If the
cornea gets too thick, it changes the
way light bends and focuses on your
retina and affects vision.

Is there a difference between
wearing daily contact lenses and
extended-wear contact lenses?

If you have something in your eye
like a contact lens, which is a very
thin piece of hydrogel, and you are
walking around wearing that same
lens every day, you don’t really
know what it comes into contact
with and what it picks up. There are
lots of things floating around in the
air, like viruses, bacteria, fungi and
spores. Especially here in Southeast
Asia, where the weather is
wonderful for all types of microorganisms
to live. On the other
hand, if you change your lenses,
you have thrown out all the bad
stuff and you have nice clean lenses
to wear.

Do cleaning solutions for contact
lenses help?

They work pretty well but at the
end of the day, you can say we are
all human and we are sloppy with
that. When we do studies on contact-
lens cases, we find a lot of
them have bugs growing in them.

What’s in a human teardrop?

They act as both a delivery and
an excretory route for nutrients
and metabolic products of the
cornea.

During waking hours, the delivery
of tears is continuous, but
fresh fluid remains in parts of the
eye until after the next blink,
when fluid is drawn to form what
is called the tear film or tear layer.

The stability of the tear layer is
important for maintaining the
health of the eye.

With age, the volume of tears
and the levels of the major tear
proteins in them tend to decline,
which result in drier eyes.

Scientists have studied tears,
using them as reference points to
measure the health of the eye.

They have also studied the chemicals
in them.

One study, for instance, found
that a woman’s tears of sadness may temporarily lower a man’s
testosterone level. The researchers
from Israel found that
men who sniffed the tears became
less sexually aroused than
when they sniffed saline solution.